1. Field of the Invention
The invention relates generally to the fabrication of semiconductor devices and to polishing and planarizing of substrates.
2. Background of the Related Art
Reliably producing sub-half micron and smaller features is one of the key technologies for the next generation of very large scale integration (VLSI) and ultra large scale integration (ULSI) of semiconductor devices. However, as the fringes of circuit technology are pressed, the shrinking dimensions of interconnects in VLSI and ULSI technology has placed additional demands on the processing capabilities. The multilevel interconnects that lie at the heart of this technology require precise processing of high aspect ratio features, such as vias, contacts, lines, and other interconnects. Reliable formation of these interconnects is important to VLSI and ULSI success and to the continued effort to increase circuit density and quality of individual substrates and die.
In the fabrication of integrated circuits and other electronic devices, multiple layers of conducting, semiconducting, and dielectric materials are deposited on from a surface of a substrate and portions of the layers may be removed. Thin layers of conducting, semiconducting, and dielectric materials may be deposited by a variety of deposition techniques. Common deposition techniques in modern processing include physical vapor deposition (PVD), also known as sputtering, chemical vapor deposition (CVD), plasma-enhanced chemical vapor deposition (PECVD), and now electro-chemical plating (ECP).
As layers of materials are sequentially deposited and removed, the uppermost surface of the substrate may become non-planar and require planarization prior to subsequent processing. Planarizing a surface, or xe2x80x9cpolishingxe2x80x9d a surface, is a process where material is removed from the surface of the substrate to form a generally even, planar surface. Planarization is useful in forming features on a substrate by removing excess deposited material used to fill the features and to provide an even surface for subsequent levels of metallization and processing. Planarization is also useful in removing undesired surface topography and surface defects, such as rough surfaces, agglomerated materials, crystal lattice damage, scratches, and contaminated layers or materials.
Chemical mechanical planarization, or chemical mechanical polishing (CMP), is a common technique used to planarize substrates. CMP utilizes a chemical composition, typically a slurry or other fluid medium, for selective or non-selective removal of material from a substrate surface. In conventional CMP techniques, a substrate carrier or polishing head is mounted on a carrier assembly and positioned in contact with a polishing pad in a CMP apparatus. The carrier assembly provides a controllable pressure to the substrate urging the substrate against the polishing pad. The pad is moved relative to the substrate by an external driving force. The CMP apparatus effects polishing or rubbing movement between the surface of the substrate and the polishing pad while dispersing a polishing composition, or slurry, to effect chemical activity and/or mechanical activity and consequential removal of material from the surface of the substrate.
Conventional CMP processes are performed using an abrasive article, such as a polishing composition, or slurry, containing abrasive particles in a reactive solution with a conventional polishing pad. Alternatively, the abrasive article can be a fixed abrasive article, such as a fixed abrasive polishing pad, which may be used with a CMP composition or slurry that does not contain abrasive particles. A fixed abrasive article typically comprises a backing sheet with a plurality of geometric abrasive composite elements adhered thereto. Additionally, polishing compositions without abrasives, or abrasive-free compositions, may be used with polishing media free of abrasive articles to polish a substrate surface.
Conventionally, in polishing substrates having features, such as a dual damascenes features formed by the deposition of a barrier layer in an aperture and a conductive material, for example copper, disposed on the barrier layer formed thereon, the conductive material is polished to the barrier layer, and then the barrier layer is polished to the underlying dielectric layer to form the feature. One challenge that is presented in polishing conductive materials is that the interface between the conductive material and the barrier layer is generally non-planar. Further, the conductive material and the barrier materials are often removed from the substrate surface at different rates, both of which can result in excess conductive material being retained as residues on the substrate surface.
Additionally, substrate surfaces may have different surface topography, depending on the density or size of features formed therein, which makes effective conformal removal of excess conductive material from the substrate surface difficult to achieve. For example, it has been observed that excess conductive material from one area of the substrate surface having a dense feature area is removed at a slower removal rate, and with residual copper material remaining after polishing, as compared to removing copper material from a substrate surface area having few, if any, features formed therein, and minimal or reduced excess conductive material residues.
To ensure removal of all the excess conductive material and residues before removing the barrier material, it is necessary to overpolish the copper and the interface. Overpolishing of copper and the interface can result in forming topographical defects, such as concavities or depressions, referred to as dishing, and can further lead to non-uniform removal of the barrier layer disposed thereunder. Additionally, overpolishing can result in erosion, the excessive removal of dielectric material surrounding a feature.
One proposed solution to reduce dishing and erosion is the use of pressure sensitive slurries, also known as non-Prestonian slurries. Prestonian slurries are broadly defined as slurries that have a removal rate proportional to both the contact pressure between the substrate and platen and the polishing speed of the platen. Non-Prestonian slurries have removal rates that are not proportional to the polishing pressure and the polishing speed. For example, a non-Prestonian slurry may have a linear correlation between removal rate and polishing pressure, but may reach a range of polishing pressures, typically at decreasing polishing pressures, which results is no noticeable removal of material from the substrate surface.
FIG. 1 shows a comparison between Prestonian slurry A, typically a conventional polishing slurry, and non-Prestonian slurry B. The Prestonian slurry A is shown with a polishing rate having a constant linear slope or removal rate versus polishing pressure (or polishing speed), while the non-Prestonian slurry B has a polishing rate with a variable linear slope, indicted by a period of no noticeable removal rate followed by a sudden increase in removal rate versus polishing pressure during the application of increasing polishing pressure.
It has been observed that the pressure sensitive slurries are insensitive to overpolishing and exhibit reduced or minimal dishing or erosion of substrate features. However, pressure sensitive slurries have difficulty removing residual amounts of copper containing material from a substrate surface even under extreme amounts of overpolishing.
Therefore, there exists a need for a polishing method and related polishing composition that facilitates the removal of residual amounts of copper containing material from a substrate surface.
The invention generally provides a method and composition for planarizing a substrate surface with reduced or minimal residue remaining from polishing processes. In one aspect, a composition is provided for planarizing a substrate including a pressure sensitive solution and one or more chemical agents for complexing with a metal or oxidized metal, wherein the complexing agent is selected from the group of ammonium salts of organic acids, amines, amine derivatives, compounds with one or more peroxy acid groups, ions of at least one transition metal, and combinations.
In another aspect, a method is provided for planarizing a substrate surface, comprising applying a composition to a polishing media, the composition including a pressure sensitive solution and one or more chemical agents for complexing with a metal or oxidized metal, wherein the complexing agent is selected from the group of ammonium salts of organic acids, amines, amine derivatives, compounds with one or more peroxy acid groups, ions of at least one transition metal, and combinations, and polishing the substrate surface.
In another aspect, a method is provided for removal of a copper containing layer from a substrate surface including applying a composition to a polishing media, the composition including a pressure sensitive solution, between about 1 wt. % or less of a solution containing ammonium salts of organic acids, about 10 wt. % or less abrasive particles, and polishing the substrate surface with the polishing media. The solution containing ammonium salts of organic acids may include up to about 40 wt. % citric acid, up to about 5 wt. % ammonium hydroxide, deionized water, and a pH between about 3 and about 7.